Overflowing Toilet

It has a Wirquin JollyFill flush system....so as per instructions (see attached) I took the diaphragm washer out of the inlet and gave it a good clean. It stopped the water from overflowing at the top of the cistern and massively reduced overflow.

However, the water stops coming into cistern once the float rises up, but then about 5 mins later water starts trickling into the toilet pan (a very small amount, especially compared with before).....does this mean there is just a small adjustment I need to make somewhere or do I need to take the whole toilet away from the wall (we have a closed couple toilet) to access the filter and give that a clean???